This invention relates to an improved ring lighting for microscopes, more particularly microscopes such as those used for examination, more particularly as regards the purity of precious stones.
It is known that such lighting for microscopes is extremely important since, for a good observation of the inclusions present in a precious stone, structural phenomena such like, and any hindering light effect among other things as a result of reflection on the polished facets of the precious stone must be avoided.
For this purpose, there has already been used for a long time a kind of lighting, more particularly a so-called dark ground lighting comprising substantially a lighting screened for the eye, a black background provided under the diamond so that the light is located on the side of the precious stone, thereby impinging the said precious stone from a direction which is more or less perpendicular to the observation direction.
The major drawback of said known dark ground lighting lies principally in that the light intensity thereof is too weak to allow an optimum observation.
It has also already been proposed to improve the light intensity, e.g. by using a lamp having a higher wattage, but other drawbacks result therefrom such as a too important heat evolution, a warm air stream along the precious stone, thereby forming heat vibrations hindering the observation around the precious stone, etc.
In order to prevent these last drawbacks, it has also already been suggested to use a lamp having a higher wattage with a suitable cooling system, but the drawback thereof lies in a very expensive device.